1. Field of the Invention
The invention is directed to a shielding for openings in shielded housing, particularly for shielding the viewing opening of a monitor, using soft-magnetic materials in combination with an electrical coil for compensating noise fields, the current of the coil being set dependent on the influencing magnetic field.
2. Description of the Prior Art
For shielding electromagnetic devices, European Application 250 250 discloses surrounding the device with a shielding housing of a hardenable compound, which can be electrically conductive or soft-magnetic due to inclusions of metals or due to a metal coating. For shielding the opening, for example the viewing opening of a monitor or of a television set, this European application that a shield of transparent material be employed which, for example, can comprise a metal coat. Such a shielding for the viewing opening of a monitor, however, has the disadvantage that either the metal coat must be kept extremely thin or the metal coat must be applied in the form of lattice in order to retain good light transmissivity. In any case, the light transmissivity is degraded, this being particularly unbeneficial for color monitors that are present in spaces having strong magnetic fields.
For shielding rooms, it is likewise generally known from German OS 21 46 071 to provide a coil system that is supplied with a current via sensors dependent on the magnetic field. This current is controlled such that the magnetic field it generates is directed oppositely to the disturbing magnetic field.
German OS 24 46 986 also discloses that such known electrical coils influenced by magnetic field sensors additionally be provided in rooms shielded by soft-magnetic or electrically conductive material in order to improve the shielding effect.